With the increasing bandwidth requirements caused by the increase in people's demand for voice, data, multimedia, and other services, the OTN has gradually become a core platform for bearer services of various operators. Transmission of 10 Gigabit (10G) Ethernet service data on the OTN is currently considered a hot topic.
FIG. 1 is a schematic structural view of an OTN frame. As shown in FIG. 1, the OTN frame includes an optical channel payload unit-k (OPUk) payload, an optical channel transport unit-k (OTUk) forward error correction (FEC), and the following overhead (OH) portion caused by transmitting the payload:
OPUk OH; optical channel data unit-k (ODUk) OH; and OTUk OH.
FIG. 2 is a schematic view of an OH structure of the OTN frame shown in FIG. 1. Referring to FIG. 2, a client specific portion is set at positions corresponding to 15th and 16th bytes. The portion contains a payload structure identifier (PSI) occupying one byte.
OPU types and capacity corresponding to the OPUk are as shown in Table 1.
TABLE 1OPU Payload bit rateOPU typeOPU Payload nominal bit ratetoleranceOPU12 488 320kbit/s±20 ppmOPU2238/237 × 9 953 280kbit/sOPU3238/236 × 39 813 120kbit/sOPU1-XvX * 2 488 320kbit/s±20 ppmOPU2-XvX * 238/237 * 9 953 280kbit/sOPU3-XvX * 238/236 * 39 813 120kbit/sNOTEThe nominal OPUk Payload rates are approximately: 2 488 320.000 kbit/s (OPU1 Payload), 9 995 276.962 kbit/s (OPU2 Payload) and 40 150 519.322 kbit/s (OPU3 Payload). The nominal OPUk-Xv Payload rates are approximately: X * 2 488 320.000 kbit/s (OPU1-Xv Payload), X * 9 995 276.962 kbit/s (OPU2-Xv Payload) and X * 40 150 519.322 kbit/s (OPU3-Xv Payload).
It can be seen that, the payload bandwidth of the OPU2 is 9.995276962 GBits/s.
In order to transmit 10G Ethernet code blocks (containing data and control codes), a payload bandwidth of at least 10 GBits/s is required. However, the payload bandwidth of the OPU2 of the OTN is 9.995276962 GBits/s, smaller than 10 GBits/s, and thus cannot meet the payload bandwidth requirements for transmission of 10G Ethernet frames in the OTN. Therefore, some companies proposed to extend the payload bandwidth of the OPU by using a portion of unused OPU and ODU overheads.
It can be seen from FIG. 2 that, nine Reserve (RES) bytes, namely, the first three RES bytes in the second row and six RES bytes in the fourth row in FIG. 2, may be used for bearing the load. Comparing FIG. 1 with FIG. 2, it can be seen that a portion in FIG. 2 corresponding to the OPUk OH in FIG. 1 includes a client specific portion and a PSI, and occupies eight bytes, in which the PSI occupies one byte and cannot be used for bearing the load, and the other seven bytes may be used for bearing the load. In this way, the 16 bytes may be used for bearing the load, thereby extending the payload bandwidth of the OPU2.
After the payload bandwidth of the OPU2 is extended, the payload bandwidth of the OPU2 may be increased to (3808*4+16)/(3808*4)*9.995276962 GBits/s=10.005776202 GBits/s. The value is slightly higher than the rate of 10 GBits/s. Currently, 10G Ethernet signals are generally encoded through a 64B/66B encoding scheme, and the linear rate obtained after encoding is (66/64)*10 GBits/s=10.3125 GBits/s, which is still larger than the extended payload bandwidth of the OPU2. It can be seen that, the payload bandwidth requirements for transmission of 10G Ethernet standard MAC frames in the OTN cannot be met, even if the 64B/66B encoding scheme is used, and the encoding rate of 10G Ethernet code blocks needs to be reduced to be lower than the minimum payload bandwidth of the OPU2.
Although the payload bandwidth requirements for transmission of the 10G Ethernet code blocks in the OTN can be met after the encoding rate of the 10G Ethernet code blocks is reduced to be smaller than the minimum payload bandwidth of the OPU2, no specific solution for mapping the 10G Ethernet code blocks to the OTN for transmission is provided currently.